1. Field of the Invention
The present invention relates to an apparatus and a method for indicating uplink resource allocation in a broadband wireless communication system. More particularly, the present invention relates to an apparatus and a method for avoiding resource loss when only burst allocation of a particular characteristic (e.g., a long Transmission Time Interval (TTI)) in a Time Division Duplex (TDD) frame including asymmetric links is considered and for indicating burst allocation of various characteristics without additional signaling overhead.
2. Description of the Related Art
A 4th Generation (4G) communication system, which is a next-generation communication system, aims to provide users with services of various Quality of Service (QoS) levels at a data rate of about 100 Mbps. 4G representative communication systems include an Institute of Electrical and Electronics Engineers (IEEE) 802.16 system. The IEEE 802.16 system adopts an Orthogonal Frequency Division Multiplexing (OFDM)/Orthogonal Frequency Division Multiple Access (OFDMA) scheme to support a broadband transmission network over a physical channel.
Broadband wireless communication systems, such as the IEEE 802.16 system, divide one frame into a plurality of subframes in order to support various wireless and service environments.
FIG. 1 illustrates a basic frame structure of an IEEE 802.16 m system according to the related art.
Referring to FIG. 1, an IEEE 802.16 m system uses frames based on a superframe 100. The superframe 100 includes a plurality of (e.g., four) frames 110, and the frame 110 includes a plurality of (e.g., eight) subframes 120. In a Time Division Duplex (TDD) frame structure, some (e.g., five) subframes 120 in the frame 110 are operated as DownLink (DL), and the other (e.g., three) subframes 120 are operated as UpLink (UL). A gap (e.g., Transmit/receive Transition Gap (TTG), Receive/transmit Transition Gap (RTG)) for switching is interposed between the links.
Based on such a frame structure, the broadband wireless communication system takes account of burst transmission in each subframe to support short latency, which is referred to as a default Transmission Time Interval (TTI) transmission. The broadband wireless communication system provides the burst transmission of various lengths for the efficient burst transmission according to various wireless and service environments. Specifically, the IEEE 802.16 m system considers the burst transmission length of two characteristics including the default TTI and a long TTI. As stated above, the default TTI indicates the transmission in one subframe and the long TTI indicates the transmission over the plurality of the subframes. In the IEEE 802.16 m system, the length of the long TTI is four frames in a case of a Frequency Division Duplex (FDD) system, and the entire length of the DL or the UL in a case of the TDD system. More particularly, in the D:U TDD system, the length of the DL long TTi is D-ary subframes and the length of the UL long TTI is U-ary subframes.
Burst allocation information of the various transmission lengths is transmitted to a terminal over a DL control channel called an Advanced-MAP (A-MAP) which is provided in the DL subframe. The allocation information includes an Information Element (IE) called A-MAP IE. To indicate the UL default TTI in a certain DL subframe, it is necessary to indicate the UL subframe location including the burst allocation. To indicate a certain UL subframe location in one DL subframe, a number of bits enough to indicate the whole UL subframe index are required. More particularly, when the total number of the UL subframes is eight at maximum, three bits are needed. In addition, one more bit is required to indicate whether the corresponding UL allocation is the long TTI or the default TTI. Namely, signaling overhead of about four bits is required to indicate the burst allocation of the various characteristics in the certain DL subframe.
The A-MAP IE for indicating the burst allocation in the IEEE 802.16 m system includes basic assignment A-MAP IE, persistent assignment A-MAP IE, group assignment A-MAP IE, and Code Division Multiple Access (CDMA) allocation A-MAP IE according to the burst allocation characteristics. The A-MAP IE further includes subband A-MAP IE for discontinuous resource allocation, and feedback polling IE for transmitting feedback information, such as Multiple-Input Multiple-Output (MIMO) feedback. Most of the A-MAP IEs are 56 bits in size (e.g., considering 16-bit Cyclic Redundancy Check (CRC)), the actual information bits are 40 bits) to reduce the decoding complexity. The variable-sized A-MAP IE, such as feedback polling IE, is split and then transmitted. As such, to efficiently fix the size of the A-MAP IE, a method for reducing the signaling overhead is needed.
In this regard, the IEEE 802.16 m system predefines the number and the location of the UL subframes corresponding to the certain DL subframe so as to reduce the signaling overhead. That is, the locations of the subframes for the burst allocation indicated by the A-MAP IEs in the DL subframe are predefined. This correspondence varies based on the ratio of the DL to the UL.
When the single UL subframe corresponds to one or more DL subframes, the UL subframe for the burst allocation indicated by the A-MAP IE transmitted in the DL subframe can be located based on the predefined correspondence without a specific indicator. For example, in the 5:3 TDD frame structure, the DL0 subframe and the DL1 subframe correspond to the UL0 subframe, the DL2 subframe corresponds to the UL1 subframe, and the DL3 subframe and the DL4 subframe correspond to the UL2 subframe. When one DL subframe corresponds to one UL subframe, the UL subframe for the burst allocation indicated by the A-MAP IE sent over the DL subframe can be located non-explicitly. Accordingly, a particular indicator for indicating one UL subframe location in the UL subframes is unnecessary.
In contrast, when one DL subframe corresponds to the multiple UL subframes, a particular indicator is necessary to indicate one UL subframe location in the corresponding UL subframes.
FIGS. 2A and 2B illustrate a TDD frame structure when one DL subframe corresponds to multiple UL subframes in an IEEE 802.16 m system according to the related art.
Referring to FIGS. 2A and 2B, in a 3:5 TDD 802.16 m frame structure, the DL0 subframe corresponds to the UL0 subframe and the UL1 subframe, the DL1 subframe corresponds to the UL2 subframe, and the DL2 subframe corresponds to the UL3 subframe and the UL4 subframe. When one DL subframe corresponds to two UL subframes at maximum, a particular indicator is required to distinguish two UL subframes at maximum for indicating one UL subframe location among the corresponding UL subframes.
In the 5:3 TDD 802.16 e/16 m coexistence support frame structure of FIG. 2B, when the 802.16 m region occupies a D:U=1:3 region in one frame, the DL0 subframe corresponds to the UL0 subframe through the UL2 subframe. As such, when one DL subframe corresponds to three UL subframes, a particular indicator for distinguishing the three UL subframes at maximum is required to indicate one UL subframe location of the corresponding UL subframes. Herein, the indication of the certain subframe among the corresponding subframes is referred to as allocation relevance.
As the number and the location of the UL subframes corresponding to one DL subframe vary based on the ratio of the DL to the UL, the signaling (i.e., the particular indicator) is necessary to indicate the one UL subframe location amongst the corresponding UL subframes. Signaling information according to the ratio of the DL to the UL should be decoded such that the corresponding A-MAP IEs are of the fixed size. The burst transmission can have the default TTI or long TTI characteristic, which need to be distinguished.
To address those drawbacks, when one DL subframe corresponds to the multiple UL subframes in the IEEE 802.16 m system, a method for considering only the long TTI in the UL allocation is suggested to avoid the signaling overhead for the indicator which indicates the allocation relevance in the default TTI support. More specifically, when the number of the DL subframes is greater than or equal to the number of the UL frames, the 802.16 m system supports both of the default TTI and the long TTI and indicates the default TTI or the long TTI using a long TTI indicator. As for the default TTI, the corresponding subframe can be located based on the predefined correspondence. In contrast, when the number of the DL subframes is smaller than the number of the UL frames, the 802.16 m system supports the long TTI alone and the A-MAP IE includes 1-bit long TTI indicator.
FIG. 3 illustrates disadvantages in burst allocation indication of a particular characteristic in a TDD 802.16 e/16 m coexistence support frame structure when one DL subframe corresponds to multiple UL subframes in an IEEE 802.16 m system according to the related art.
Referring to FIG. 3, in a 5:3 TDD 802.16 e/16 m coexistence support frame structure, a UL control channel, such as RaNGing Channel (RNGCH) or BandWidth REQuest Channel (BW REQ CH), resides in a specific UL subframe (e.g., the first UL subframe) in a cycle, rather than in every UL frame. Herein, when only the long TTI is considered for the UL allocation, the same resource index as the resource occupied by the UL control channel in the other UL subframe is unusable according to the RNGCH or the BW REQ CH in the specific UL subframe. That is, although there is no UL control channel, the other UL subframe cannot use the same region as the resource occupied by the UL control channel for the burst allocation, which causes resource loss.
For instance, when one UL subframe includes 48 Logical Resource Units (LRUs) base on the BandWidth (BW) of 10 Mhz in the 3:5 TDD 802.16 m frame structure, four LRUs are used as the RNGCH, and the RNGCH resides in one UL subframe, the corresponding frame is subject to the resource loss of approximately 6% (=4*4/(5*48)) by considering only the long TTI for the UL allocation.
In the 5:3 TDD 802.16 e/16 m coexistence support frame structure, when the 802.16m region occupies a D:U=1:3 region in the frame, one UL subframe includes 35 LRUs based on the BW of 10 Mhz, six LRUs are used as the RNGCH, and the RNGCH resides in one UL subframe, the corresponding frame is subject to the resource loss of approximately 11% (=2*6/(35*3)) by considering only the long TTI for the UL allocation.
Therefore, a need exists for a burst allocation indication method for reducing the signaling overhead for the burst allocation indication and for avoiding the resource loss when only the burst allocation of a particular characteristic (e.g., the long TTI) is considered.